Conventional thin dielectric materials for use in capacitors or as a gate insulation layer in an FET structure are, for example, Ta2O5, Al2O3, CeO2 and SiON. A typical dielectric constant for an Al2O3 film is in the range of from 10 to 15.
Pb (Zr, Ti)O3 (PZT) is a well-known material which may find a number of different applications in the manufacture of semiconductor devices, for example as a ferroelectric material. PZT may be formed having a pyrochlore phase therein. Such a material is hereinafter referred to as “PZT pyrochlore”. In this way, films with very high dielectric constants, for example from 40 up to 100 may be provided. If a PZT pyrochlore film could be manufactured which is extremely thin, having a very smooth surface and an excellent grain uniformity then there would be clear advantages in the possibility of manufacturing high quality VLSI/ULSI devices such as capacitors, FETs and the like, having high integration density and good reliability.
Definition of the Invention
A first aspect of the present invention comprises a method of manufacturing an ultra-thin PZT pyrochlore film, the method comprising providing a structure comprising a base layer, and forming on said base layer, a titanium layer and a PZT layer in mutual contact, annealing said structure thereby forming said PZT pyrochlore layer on said base layer. Preferably, the titanium layer comprises elemental titanium or titanium oxide (TiOx).
In the method of the present invention, preferably the titanium layer is first formed above a substrate or wafer and the PZT layer is subsequently formed on top, prior to annealing. However, the reverse situation (deposition of PZT before the Ti layer) is also within the ambit of the present invention.
Optimally, for good smoothness, the ratio of the thickness of the titanium layer to that of the PZT layer, is 1:3 or more, preferably 1:2 or more, still more preferably, 1:1 or more, for example up to 1:0.1.
Typical annealing temperatures are from 400° C. to 800° C., preferably from 550° C. to 750° C.
Deposition of the layers to be annealed can be effected by conventional methods such as physical vapour deposition (PVD) or chemical vapour deposition (CVD) or spin coating. The annealing method may also be effected by conventional means, for example use of rapid thermal annealing (RTA) or in a furnace. The annealing can be carried out in many suitable atmospheres such as oxygen, air or nitrous oxide.
Preferably the Ti and PZT layers are formed on a metal layer such as Pt, Au or W.
In practice, the method of the present invention may be used to manufacture a wide range of electronic devices, for example capacitors or active devices such as various kinds of FET.
Another aspect of the present invention therefore provides a method of manufacturing a capacitor, the method comprising forming a lower electrode layer, forming in mutual contact, a titanium layer and a PZT layer, performing an annealing step so that a PZT pyrochlore dielectric layer is formed from said titanium layer and said. PZT layer and forming an upper electrode layer above the PZT pyrochlore dielectric layer. Preferably, the titanium layer comprises elemental titanium or titanium oxide (TiOx). Another aspect of the present invention provides a method of manufacturing a field effect transistor, the method comprising forming a drain region and a source region separated by a gate region, forming a titanium layer and a PZT layer in mutual contact and at least partially overlying said gate region, performing an annealing step so that a PZT pyrochlore insulating layer is formed from said titanium layer and said PZT layer and forming a gate electrode above said PZT pyrochlore insulating layer.
Electronic devices with ultra-thin pyrochlore layers are also in themselves novel. Therefore, a further aspect of the present invention provides an electronic device comprising a PZT pyrochlore layer of no more than 20 nm thickness, preferably no more than 10 nm thickness.